Diabetes is at epidemic proportions worldwide. Reportedly, around 370 million people have diabetes and this number is increasing in every country. One of the most common and serious complications resulting from diabetes is poorly healing wounds that develop most commonly on areas of high pressure on the surface of the foot, such as under the hallux (big toe), metatarsophalangeal joints, the tops and ends of the toes, the middle and sides of the foot and the heel. Foot ulcers form as a result of nerve damage resulting in a loss of sensation over such pressure points on the foot, which leads to extended microtrauma, breakdown of overlying tissue, and eventual ulceration. In addition, this loss in sensation can allow minor scrapes or cuts to go without proper treatment and eventually lead to the formation of ulcers. A significant percentage of diabetics will develop a foot ulcer during their lifetime. Once a diabetic foot ulcer (DFU) is formed, treatment can be challenging, particularly in view of the compromised healing environment due to the presence of neuropathy, vascular disease, altered neutrophil function, diminished tissue perfusion and/or defective protein synthesis, all of which often accompany diabetes.
There is a great need for better treatment modalities for these chronic ulcerations. DFUs are a leading cause of amputation. The longer these wounds remain, the greater the opportunity for them to increase in size and depth and become infected. As a consequence, these complications result in 80,000 amputations annually in the U.S. alone. This chronic pathology also severely compromises the overall health of the patient leading to a further downward health spiral of these patients, and additional costs to the health care system; their treatment doubles the cost of care for affected diabetic patients.
The principle aim of DFU management is wound closure. Under the current standard of care, DFU wound care focuses on radical and repeated debridement, frequent inspection and bacterial control, off-loading of any pressure on the wound, and careful moisture balance to prevent maceration. Effective DFU healing, however, has not been consistently achieved through this approach, and results can depend heavily on patient compliance. As a result, adjunctive treatments have been developed to address DFUs. Consensus reports for the management of diabetic foot ulcers recommend that for ulcers showing less than 50% healing at 4 weeks following good standard wound care, advanced therapeutics should be considered in order to speed wound healing and decrease complications. Such advanced treatments include negative pressure wound therapy, biological dressings, bioengineered skin equivalents, hyperbaric oxygen therapy, platelet rich plasma and growth factors.
However, only a small number of these advanced wound-care products have been shown to accelerate DFU healing in prospective, randomized registration trials, and even some of those results have been called into question by other studies. Among the products that have been studied in prospective, randomized registration trials are included becaplermin (Regranex®; Smith and Nephew), a topical gel containing recombinant human platelet-derived growth factor B chain homodimer (rhPDGF-BB), BioChaperone PDGF-BB (Adocia, Lyon, France), a topical spray that includes molecules that complex with PDGF, two living skin equivalents: a bi-layered skin substitute (Apligraf®; Organogenesis, Inc., Canton, Mass.) and a human fibroblast-derived dermal substitute (Dermagraft®; Shire, Plc., Dublin, Ireland), and vacuum-assisted wound closure (V.A.C.®; KCl, San Antonio, Tex.). Other treatment modalities that have less rigorous trial data include collagen, platelet-rich plasma, silver products, hyperbaric oxygen and electrical stimulation.
Despite some favorable results from prospective, randomized registration trials for certain advanced wound-care products, their overall benefits have been disappointing, as evidenced by the continuing high amputation rates. The following results were reported in a published meta-analysis of 35 randomized, controlled trials evaluating diabetic foot ulcer advanced therapies:                Platelet-rich plasma did not improve diabetic ulcer healing compared to good standard wound care.        Dermagraft® biological skin equivalent in pooled results from three studies showed non-significant improvement compared to standard care, with ulcer healing favoring Dermagraft (35% versus 24%).        Apligraf® biological skin equivalent bi-layer has been reported to improve healing over good standard wound care (55% versus 34%, p=0.001; 2 studies).        5, Regranex® rhPDGF-BB showed improvement in the percentage of ulcers healed compared to placebo or good standard wound care (58% versus 37%, p=0.04; 7 studies).        V.A.C.® negative pressure wound therapy improved healing more than good standard wound care (43% versus 29%, p<0.05; 1 study).        There was low or insufficient evidence for all studies related to enhanced time to ulcer healing.In addition, in four studies the incidence of complete wound closure for Regranex was reported as 50% or less (48%, 50%, 44%, and 36%).        
Such advanced therapies have not resulted in a consistently effective solution to treating DFUs. In view of their mixed clinical results along with their greater product cost compared to standard therapy, none of these advanced therapies have been widely adopted as a new standard of care for treating DFUs.
As noted above, one such advanced therapy is Regranex gel (becaplerman), which consists of rhPDGF-BB at a concentration of 100 μg/g in sodium carboxymethylcellulose gel. Specifically, Regranex is formulated as a multi-use, non-sterile, low bioburden, preserved, sodium carboxymethylcellulose-based (CMC) topical gel, and is indicated for daily application to improve the healing of chronic DFUs over several months. The Regranex package insert (label) states that it should be applied daily up for up to 140 daily applications over a 20 week period, and even longer if the physician deems it appropriate at a dose equal to about 0.006 mg/cm2 (6.25 μg) of wound surface area.
Regranex remains the state-of-the-art growth factor therapy for healing of wounds, as evidenced by the fact that it is the only recombinant growth factor product to receive FDA approval for treatment of chronic wounds, even though it was FDA-approved over 15 years ago. Moreover, no one has successfully developed another formulation of Regranex (i.e. rhPDGF-BB) since its FDA approval. While clinical and non-clinical data support its clinical use, we believe Regranex has a number of limitations including: 1) the need for daily applications to the DFU by the patient, requiring daily wound dressing changes by the patient; 2) the low dosing prescribed in the FDA-approved Instructions for Use, about 0.006 mg (6 μg) per cm2 of wound surface area; 3) often imprecise dosing due to the difficulty the patient experiences in visualizing and applying the gel from a tube (similar to a toothpaste tube) onto the wound which is often located on the bottom of the foot; 4) the need to keep the product refrigerated (about 2-8° C.); 5) lack of sterility of the Regranex gel; 6) the need for prolonged patient use—up to, and potentially exceeding, 140 daily applications over about a five month period; and 7) the use of the carboxymethylcellulose-based (CMC) topical gel which lacks the ability to provide a biological matrix for cellular ingrowth.
Furthermore, Regranex has been only modestly accepted by the medical community as an effective treatment for DFUs. Following the European Medicines Agency (EMA) review of data from four Regranex efficacy clinical trials, the EMA concluded that a 30 μg PDGF/g formulation was less effective than a 100 μg PDGF/g and there was little difference between the 100 μg PDGF/g formulation and a 300 μg PDGF/g formulation. The EMA further concluded that the 100 μg PDGF/g product formulation possessed only “modest” efficacy.
Perhaps as a result of the “modest” efficacy of Regranex, the effectiveness of the active ingredient in Regranex (i.e., rhPDGF-BB) in treating wounds has been called into question. Park S A, Raghunathan V K, Shah N M, Teixeira L, Motta M J, et al. (2014) PDGF-BB Does Not Accelerate Healing in Diabetic Mice with Splinted Skin Wounds. PLoS ONE 9(8): e104447. doi:10.1371/joumal.pone.0104447, reported the results from a study using a controlled full thickness splinted excisional wound model in db/db mice (type 2 diabetic mouse model). Two splinted 8 mm dorsal full thickness wounds were made in db/db mice, and were topically treated once daily with either 3 μg PDGF-BB in 30 μl of 5% PEG-PBS vehicle or an equal volume of vehicle for 10 days. The study concluded that PDGF-BB, although bioactive in vitro, failed to accelerate wound healing in vivo in the db/db mice using the splinted wound model.
While experts in the field question the effectiveness of Regranex's active ingredient, rhPDGF-BB, Applicants believe that there are a number of reasons for Regranex's questionable efficacy. First, Regranex is delivered to the wound site by a gel carrier. This formulation allows the rhPDGF to be cleared from the site within minutes to hours. Second, while the gel carrier is biocompatible, we believe it provides no substrate for cell and vascular ingrowth and in fact may be inhibitory to cell growth and migration in the wound thereby potentially slowing the healing process and resulting in suboptimal healing. Third, Regranex is non-sterile, only stable when stored at 2-8 degrees C. (refrigerated) and must be applied daily often to hard to reach anatomical sites, all leading to poor patient compliance; Fourth, although the clinic data showed no difference between the 100 μg/g formulation and the 300 μg/g formulation, Applicants believe that the growth factor in Regranex is at too low of a concentration for optimal cell recruitment and proliferation. The Regranex dose per square centimeter of wound surface area is only 6 μg and Applicants believe that is too low for optimal cell recruitment and proliferation. Fifth and finally, despite its commercial use on patients for the past 15 years, the Applicants believe that the growth factor that is included in Regranex is not fully potent. The rhPDGF used in Regranex is recombinantly produced in a yeast expression system. When expressed in yeast, the protein is excreted as a fully folded homodimeric protein consisting of two antiparallel B chains held together by two interchain disulfide bonds. However, during fermentation, internal proteolysis (clipping between residues Arg32 and Thr33) and C-terminal truncation (Arg32 and Thr109) may occur. Internal proteolysis yields three potential forms of rhPDGF-BB: intact (both B chains are intact), single-clipped (one B chain is clipped), and double-clipped (both B chains are clipped). Clipping also creates new C-terminal sites for further C-terminal truncations and leads to a very complex mixture of isoforms. Applicants believe that the non-intact isoforms of rhPDGF-BB that are included in Regranex are far less effective in treating DFUs than the fully intact isoform.
rhPDGF-BB has also been used in orthopedic and periodontal indications, wherein the healing environments and the healing processes are very different from dermal wounds. Two such products include Augment Bone Graft and GEM21S, both of which include rhPDGF-BB as an active ingredient. GEM21S, consisting of rhPDGF-BB solution and a particulate synthetic bone substitute, was FDA-approved in 2005 and is indicated to improve bone healing in chronic periodontal defects. Augment Bone Graft also consists of rhPDGF-BB solution and a particulate synthetic bone substitute. Augment is FDA approved, based on a 434 patient pivotal clinical trial in the US and Canada, for improving bone fusion in foot and ankle fusion following a single implantation into the bone defect during surgery. However neither of these products is indicated for treating dermal wounds, such as DFU's, and both focus on using the product to promote bone growth and fusion, a very different cellular and physiologic process from skin wound healing, through a single intra-surgical application. Like Regranex, the GEM21S and Augment Bone Graft products must be stored refrigerated (about 2-8° C.) compromising user convenience and compliance.
In summary, poor patient outcomes leading to high amputation rates, and conflicting scientific analyses demonstrate that there remains a need for a more predictable, patient/user friendly and consistently effective method and therapeutic composition for promoting dermal wound healing, including treating DFU's and other types of hard to heal wounds.